Electron beam adjusting device with magnet rings of differing alnico powdered metal content

ABSTRACT

The present invention relates to an electron beam adjusting device which is attached around the neck of a color picture tube, a CRT display, etc., and aims at providing an electron beam adjusting device in which each pair of constituent magnets can be readily magnetized with minimal magnetization variations and which is less costly. The present invention provides an electron beam adjusting device having pairs of two-, four- and six-pole ring-shaped magnets formed of an alnico metal system bonded magnet material, which are attached around the neck of a cathode-ray tube, wherein the two-pole ring-shaped magnets and the four- and six-pole ring-shaped magnets are made of respective bonded magnet materials which are different in the alnico metal magnetic powder content.

TECHNICAL FIELD

The present invention relates to an electron beam adjusting device whichis attached around the neck of a color picture tube, a CRT display, etc.

BACKGROUND ART

The mainstream magnets used in color picture tubes to make electron beamadjustment are bonded magnets (resin-bonded magnets) comprising amagnetic powder, i.e., barium ferrite in general, which is bonded with aresin material. These bonded magnets suffer, however, from the problemthat since the temperature coefficient is as large as about 0.2%/°C.,the bonded magnets expand as the temperature rises, causing a reductionin the magnetization, so that undesirable color shift may occur. Incolor display tubes, the resolution is lowered by misconvergence due tothe reduction in the magnetization. This is a fatal disadvantage topicture tubes having requirements for high definition. To solve thisproblem, it is conventional practice to use a bonded magnet materialcomprising a magnetic powder of low temperature coefficient, e.g.,alnico magnetic powder, to form an electron beam adjusting device.

Incidentally, a minute observation of the action of two-pole magnets andthat of four- and six-pole magnets reveals that the amount of beam shiftmade by the two-pole magnets is several times that by the four- orsix-pole magnets. The reason for this is as follows: The two-polemagnets are used to make a color beam from each electron gun coincidentwith the axis of the picture tube, and it is also necessary to considervariations in production of picture tubes and the effect of the earthmagnetism. Therefore, the amount of beam shift in the two-pole magnetsis set to about 9 mm in radius. In contrast, for the four- and six-polemagnets, since these are used to converge the color beams in the centerof the picture tube and the convergence of the color beams is mostlydetermined by the design of the electron guns, the amount of beam shiftis set to about 3 mm in radius.

In view of the fact that the magnitude of beam shift is proportional tothe magnetization of the magnet (i.e., the beam shift is about 1 mm to amagnetization of 1 G), it will be understood that it is sufficient andpreferable to set the magnetization of the four- and six-pole magnets toa value lower than that of the two-pole magnets.

In regard to the magnetization characteristics of alnico magneticpowder, since the coercive force of this material is smaller than thatof the conventional barium ferrite magnetic powder, it is difficult tocontrol the level of magnetization for each pair of magnets. Inparticular, in the case of magnetization at low level, variations in theamount of magnetization are likely to occur, raising difficulty inmaking convergence adjustment; in the worst case, fatal problems arise,including a failure to effect the convergence adjustment.

In addition, since alnico magnetic powder is considerably costly ascompared with barium ferrite magnetic powder, an increase in the alnicomagnetic powder content leads to a rise in the production cost.

In view of the above-described circumstances, it is an object of thepresent invention to provide an electron beam adjusting device in whicheach pair of constituent magnets can be readily magnetized with minimalmagnetization variations and which is less costly.

DISCLOSURE OF THE INVENTION

The present invention provides an electron beam adjusting device havingpairs of two-, four- and six-pole ring-shaped magnets formed of analnico metal system bonded magnet material, which are attached aroundthe neck of a cathode-ray tube, wherein the two-pole ring-shaped magnetsand the four- and six-pole ring-shaped magnets are made of respectivebonded magnet materials which are different in the alnico metal magneticpowder content, thereby solving the problems of the conventionalelectron beam adjusting device in which all the magnets are made of abonded magnet compound having a uniform alnico content.

In the electron beam adjusting device of the present invention, thealnico magnetic powder contents in the pairs of two-, four- and six-polering-shaped magnets are set in accordance with the amounts ofmagnetization required therefor, respectively, thereby making itpossible to lower magnetization variations and minimize the amount ofalnico magnetic powder used and hence possible to lower the productioncost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of one embodiment of the electron beam adjustingdevice according to the present invention;

FIG. 2 is an exploded perspective view of the embodiment;

FIGS. 3(I), 3(II) and 3(III) illustrate the arrangements of two-, four-and six-pole magnets, respectivelyp

FIG. 4 is a graph showing the dependence of the magnetic flux density onthe magnetizing voltage in the process of magnetizing two-pole magnets;

FIG. 5 is a graph showing the dependence of the magnetic flux density onthe magnetizing voltage in the process of magnetizing four-pole magnets;and

FIG. 6 is a graph showing the dependence of the magnetic flux density onthe magnetizing voltage in the process of magnetizing six-pole magnets.

BEST MODE FOR CARRYING OUT THE INVENTION

The electron beam adjusting device according to the present inventionwill be described below in detail by way of one embodiment illustratedin the drawings.

FIG. 1 is a front view of the electron beam adjusting device, and FIG. 2is an exploded perspective view of the device. In these figures, aholder 1 made of a plastic material has a threaded portion 2 at one endthereof. The holder 1 also has a ring-shaped support 3 formed on itsintermediate part as an integral part thereof. Onto the holder 1 aresuccessively fitted a pair of two-pole ring-shaped magnets (puritymagnets) 4, a ring-shaped spacer 5, a pair of ring-shaped six-polemagnets (convergence magnets) 6, a ring-shaped spacer 7, a pair ofring-shaped four-pole magnets (convergence magnets) 8, and a ring-shapedspacer 9 in the mentioned order, and finally, a lock ring 10 is broughtinto thread engagement with the threaded portion 2, thereby securing themagnets. It should be noted that when the lock ring 10 is untightened,the two-, four- and six-pole magnets on the holder 1 are rotatable foradjustment. In addition, the spacers 5, 7 and 9 have projections 11formed on the respective inner edges and the projections 11 are engagedwith a groove 12 provided on the holder 1 to prevent rotation of thespacers 5, 7 and 9.

In the above-described arrangement of the electron beam adjustingdevice, according to the present invention, a difference is made betweenthe alnico magnetic powder contents in bonded magnet materials which arerespectively used to form the two-pole magnets 4 and the six- andfour-pole magnets 6 and 8. Thus, the alnico magnetic powder content ofeach pair of magnets is set in the light of the amount of magnetizationrequired therefor, thereby facilitating the magnetization of each pairof magnets and eliminating magnetization variations. In particular, thealnico magnetic powder content in the bonded magnet material used toform the four- and six-pole magnets 8 and 6 is lowered to therebystabilize the low-level magnetization of these magnets.

To confirm the results of the invention, the present inventors madetwo-pole magnets and four- and six-pole magnets using bonded magnetmaterials different in the alnico magnetic powder content, magnetizedthem, and measured the dependence on the magnetizing voltage, andfurther compared it with the magnetizing voltage dependence ofconventional magnets all having the same alnico magnetic powder content.As an example of the present invention, the present invention formed atwo-pole magnet 4 by using an alnico metal system bonded magnet compoundhaving a relatively high alnico magnetic powder content, set to 60% byweight, and six- and four-pole magnets by using an alnico metal systembonded magnet compound having a relatively low alnico magnetic powdercontent, set to 30% by weight. As a comparative example, four- andsix-pole magnets were made of an alnico metal system bonded magnetcompound having an alnico magnetic powder content set to 60% by weight,together with a two-pole magnet made of an alnico metal system bondedmagnet compound having an alnico magnetic powder content set to 30% byweight. In both the example of the invention and the comparativeexample, the two-, four- and six-pole magnet moldings had respectiveconfigurations (outer diameter: 45 mm; inner diameter: 33.5 mm; andthickness: 1.3 mm) such as those shown in FIG. 3, and each magnetmolding was magnetized with a magnetizing yoke wound with 8 turns of awinding conductor having a diameter of 1.0 mm, using a power supply witha condenser capacitance of 500 μF, and with the charging voltage beingvaried, thereby measuring a curve representing the relationship betweenthe charging voltage and the magnetic flux density. The results of themeasurement are shown in FIG. 4.

FIGS. 4, 5 and 6 each show the dependence of the magnetic flux densityon the magnetizing voltage obtained on the basis of the measured values:FIG. 4 shows the magnetization curve of the two-pole magnets; FIG. 5shows the magnetization curve of the four-pole magnets; and FIG. 6 showsthe magnetization curve of the six-pole magnets. The curves shown by oin the figures represent the characteristics of the magnets having analnico magnetic powder content of 60% by weight, whereas, the curvesshown by • in the figures represent the characteristics of the magnetshaving an alnico magnetic powder content of 30% by weight. The point"standard" on the axis of ordinates shows the magnetic flux densityrequired for each magnet. For the two-pole magnets, the standardmagnetic flux density is defined as 9 G in the center of the magnet,whereas for the four- and six-pole magnets, it is defined as 3 G at aposition 7.5 mm from the center of the magnet.

As will be clear from the graphs, since the alnico metal system bondedmagnet compound has a small coercive force, when the high alnico contentcompound is used, the response of the magnetic flux-density to thechange of the charging voltage is extremely steep in the low magneticflux density region; therefore, in the case of magnetization ofrelatively low level as in the four- and six-pole magnets, slight supplyvoltage fluctuations lead to variations in the amount of magnetization,thus making it difficult to perform stable magnetization. In contrast,in the example of the present invention, in which the four- and six-polemagnets has a relatively low alnico magnetic powder content, theresponse of the magnetic flux density to the change of the chargingvoltage is extremely stable, so that it is possible to effect givenmagnetization under very stable conditions.

INDUSTRIAL APPLICABILITY

The present invention provides an electron beam adjusting device havingpairs of two-, four- and six-pole ring-shaped magnets formed of analnico metal system bonded magnet material, which are attached aroundthe neck of a cathode-ray tube, wherein the alnico metal magnetic powdercontent in the bonded magnet material used for forming each pair ofmagnets is individually set in accordance with the amount ofmagnetization required therefor, and in particular, the alnico magneticpowder content in the bonded magnet material for forming the four- andsix-pole magnets is set to a relatively low level, so that it ispossible to magnetize the four- and six-pole magnets, which require arelatively low magnetization, under stable conditions without invitingmagnetization variations. Moreover, since it is possible to minimize theamount of alnico magnetic powder (which is costly) used, an electronbeam adjusting device can be obtained at lower cost. Thus, it ispossible to provide an electron beam adjusting device which isparticularly suitable for high definition picture tubes and picturetubes of large calorific value.

What is claimed is:
 1. An electron beam adjusting device having pairs oftwo-, four- and six-pole ring-shaped magnets formed of an alnico metalsystem bonded magnet material having an alnico metal magnetic powdercontent, which are attached around the neck of a cathode-ray tube,wherein said two-pole ring-shaped magnets are made of bonded magnetmaterials which have a different wt % of the alnico metal magneticpowder than the wt % of the alnico metal magnetic powder of said four-and six-pole ring-shaped magnets.
 2. An electron beam adjusting deviceaccording to claim 1, wherein the wt % of the Alnico metal magneticpowder in the two-pole ring-shaped magnets is greater than the wt % ofthe Alnico metal magnetic powder in said four- and six-pole ring-shapedmagnets.
 3. An electron beam adjusting device according to claim 2,wherein the four- and six-pole ring-shaped magnets have the same wt % ofalnico metal magnetic powder.
 4. An electron beam adjusting deviceaccording to claim 3, wherein said two-pole magnet has an alnico metalmagnetic powder concentration of 60% by weight, and said four- andsix-pole magnets each have an alnico metal magnetic powder concentrationof 30% wt.
 5. An electron beam adjusting device having pairs of two-,four- and six-pole ring-shaped magnets formed of an alnico metal systembonded magnet material having an alnico metal magnetic powder contents,which are attached around the neck of a cathode-ray tube, wherein saidtwo-pole ring-shaped magnets are made of bonded magnet materials whichare different in the alnico metal magnetic powder content, and whereinthe alnico metal magnetic powder content in the bonded magnet materialfor forming said two-pole magnets is at least 30% by weight higher thanthe alnico metal magnetic powder content in the bonded magnet materialfor forming said four- and six-pole magnets.